According to the state of the art, automatic transmissions, particularly for motor vehicles, comprise planetary gear sets, which are shifted using friction elements and/or control elements, such as clutches and brakes, and which are typically connected to a starting element that is subject to a slip effect and optionally provided with a converter lock-up clutch, for example a hydrodynamic torque converter or a fluid clutch.
A transmission of this type is described in EP 0 434 525 A1. It comprises essentially one input shaft and one output shaft, which are disposed parallel to each other, a double planetary gear set concentric with the output shaft, and five control elements in the form of three clutches and two brakes, the selective operation of which, in pairs, determines different gear ratios between the input shaft and the output shaft. This transmission has a front-mounted gear set and two power paths, so that by the selective engagement in pairs of the five control elements, six forward gears are obtained.
In the first power path, two clutches are required for transmitting the torque from the front-mounted gear set to two elements of the double planetary gear set. These elements are provided in the power flow direction substantially behind the front-mounted gear set in the direction of the double planetary gear set. In the second power path, a further clutch is provided, which detachably connects this path with a further element of the double planetary gear set. The clutches are disposed such that the inner disk carrier forms the output end.
Furthermore, from the published prior art document U.S. Pat. No. 6,139,463 a compact multi-speed transmission in planetary design, particularly for a motor vehicle, is known, which has two planetary gear sets and one front-mounted gear set as well as three clutches and two brakes. In this known multi-speed transmission, two clutches C-1 and C-3 are provided in a first power path for transmitting torque from the front-mounted gear set to the two planetary gear sets. The outer disk carrier and/or the cylinder or piston and pressure compensation sides of the clutch C-3 are connected with a first brake B-1. Furthermore, the inner disk carrier of the third clutch C-3 is connected to the cylinder and/or piston and pressure compensation sides of the first clutch C-1, the inner disk carrier of the first clutch. C-1 being disposed on the output side and connected to a sun gear of the third planetary gear set.
From DE 199 49 507 A1 by the applicant, a multi-speed transmission is also known, according to which on the drive shaft two non-shiftable, front-mounted gear sets are provided, which on the output side generate two rotational speeds which, in addition to the rotational speed of the input shaft, can be switched by selectively engaging the control elements with a shiftable double planetary gear set that acts upon the output shaft, such that, for changing from one gear to the next higher or lower gear only one of the two actuated control elements, must be engaged or disengaged.
DE 199 12 480 A1 discloses an automatically shiftable motor vehicle transmission with three carrier-mounted planetary gear sets as well as three brakes and two clutches for switching between six forward gears and one reverse gear, and with one drive shaft and one output shaft. The automatically shiftable motor vehicle transmission is configured such that the drive shaft is directly connected to the sun gear of the second planetary gear set, and that the drive shaft can be connected, via the first clutch, to the sun gear of the first planetary gear set and/or, via the second clutch, to the carrier of the first planetary gear set. Additionally or alternatively, the sun gear of the first planetary gear set can be connected, via the first brake, to the transmission housing and/or the carrier of the first planetary gear set can be connected, via the second brake, to the housing and/or the sun gear of the third planetary gear set can be connected, via the third brake, to the housing.
Furthermore, DE 102 13 820 A1 discloses a multi-speed automatic transmission, comprising a first input path T1 of a first speed ratio, an input path T2, which has a larger speed ratio than the input path T1, a planetary gear set of four elements, which are arranged, in the direction of power flow, in the order of a first element, a second element, a third element and a fourth element, a clutch C-2 that transmits rotation from the input path T2 to the first element S3, a clutch C-1 that transmits rotation from the input path T2 to the fourth element S2, a clutch C-4 that transmits rotation from the input path T1 to the first element, a clutch C-3 that transmits rotation from the input path T1 to the second element C-3, a brake B-1 that engages the fourth element, a brake B-2 that engages the second element, and an output member that is coupled with the third element R3.
Within the scope of DE 101 15 983 A1 by the applicant, a multi-speed transmission is described, comprising a drive shaft that is linked with a front-mounted gear set, an output shaft that is connected with a rear-mounted gear set, and a maximum of seven control elements, through the selective shifting of which at least seven forward gears can be shifted without range shifting. The front-mounted gear set is formed by a front-mounted planetary gear set or a maximum of two non-shiftable front-mounted planetary gear sets that are linked with the first front-mounted planetary gear set, wherein the rear-mounted gear set is configured as a two-carrier four-shaft transmission with two shiftable rear-mounted planetary gear sets and has four free shafts. The first free shaft of this two-carrier four-shaft transmission is connected with the first control element, the second free shaft with the second and third control elements, the third free shaft with the fourth and fifth control elements, and the fourth free shaft is connected with the output shaft. According to the invention, a multi-speed transmission with a total of six control elements is proposed, which connect the third free shaft or the first free shaft of the rear-mounted gear set additionally with a sixth control element. For a multi-speed transmission with a total of seven control elements, it is proposed according to the invention that the third free shaft is additionally connected with a sixth control element D′ and the first free shaft additionally with a seventh control element.
Furthermore, the scope of DE 101 15 987 by the applicant describes a multi-speed transmission with at least seven gears. In addition to the input shaft and the output shaft, this transmission comprises a non-shiftable front-mounted gear set and a shiftable rear-mounted gear set in the form of a two-carrier four-shaft transmission. The front-mounted gear set comprises a first planetary gear set, which, in addition to the input rotational speed of the input shaft, also provides a second rotational speed, each of which may optionally be shifted to a rear-mounted gear set. The rear-mounted gear set comprises two shiftable planetary gear sets, which can shift at least seven gears using the six control elements, forming two power paths. During each shifting operation, range shifting is advantageously avoided. A 9-gear multi-speed transmission is further known from DE 29 36 969; it comprises eight control elements and four gear sets.
Automatic vehicle transmissions in planetary design in general have previously been described in the prior art on many occasions and undergo continuous developments and improvements. These transmissions should have, for example, a sufficient number of forward gears as well as one reverse gear and a gear ratio that is excellently suited for motor vehicles, having a high overall spread as well as favorable progressive ratios. Furthermore, they should have a high starting gear ratio in the forward direction and should include a direct gear, and should additionally be suited for use both in passenger cars and in commercial vehicles. In addition, these transmissions should have a low complexity, in particular they should require a small number of control elements, and should avoid double-shifts when shifting sequentially, so that always only one control element is engaged when shifting in defined gear groups.